A phoswich multidetector probe for measuring tracheal mucus velocity

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Abstract
A simple, reliable, compact and sensitive detection system was required to measure the position as a function of time of local concentrations of tracers tagged with 99mTc as they are transported up the trachea by mucociliary activity. A multidetector probe to meet these requirements was designed and constructed: it consists of 3 pairs of NaI(Tl)/CsI(Na) phoswich sandwiches arranged in line so that measurements of response in 6 positions can be made. Each crystal was 8 mm thick, 1.5 mm deep and formed an arc of 90.degree. with an internal radius of 7 cm. Spatial resolution and background reduction were achieved by pulse height and pulse shape analysis and the use of tungsten parallel-plate collimators. At the face of the collimators the system had a spatial resolution of 9 mm FWHM and a sensitivity of 3.78 .times. 10-2 CPS Bq-1 (1400 CPS .mu.Ci-1). Background radiation resonse was typically 1 CPS per crystal. Determinations of tracheal mucus velocity were made in man. This multidetector probe could be adapted to other velocity measurements over an extended range and for the measurement of activity profiles when high sensitivity is desired.